1. Field of the Invention.
This invention relates to a downhole heating generator for producing hot water or steam in oil wells to aid in the recovery of oil.
2. Description of the Prior Art.
In the recovery of petroleum hydrocarbons certain geological formations may be encountered that prevent the full or an economical recovery of the petroleum. In some instances the viscosity of the oil or petroleum also bears on recovery.
Thus, steam or hot water has in the past been applied to the downhole formation to change the oil viscosity and unplug openings making the same readily available for pumping to the surface. Such steam or hot water may be applied in both primary and secondary recovery of the petroleum.
Heretofore, heating techniques have required above ground steam generators which prepare the steam at ground level and the same is pumped downhole for dispersion into the geological foundation. One of the problems with such a method and apparatus is that the steam will become dissipated during its downward travel in the tube strings. It is estimated that if the tube strings are not insulated this process is only effective to about 2,000 feet. With an insulated tube string the efficiency will only be extended downward for another 1000 feet.
Another recognized steam technique is known as a hydrocarabon-fueled generator. This system also employs ground level equipment, but to increase the efficiency the energy must be increased by an air compressor for air and hydrocarbons to produce a dry steam at the area of contact with the formation. This process involves extremely complicated control means. In addition, the process causes serious downhole corrosion problems. This process is extremely expensive.
Finally, there is known through U.S. Pat. No. 3,420,301 a form of steam generator which may be moved downhole to the area desired. This patent discloses only concentric electrodes which are connected to a ground level electric transformer and water that is pumped to the electrode area. In principle, as the electrodes are energized the water is heated and steam produced. However, testing of the disclosure in U.S. Pat. No. 3,420,301 shows that the annular gap between the electrodes was too small to adequately heat the number of gallons per minute (GPM) necessary to create an efficient steam generator.
In view of the diameter restriction in a tube string of an oil well there must also be a diameter restriction in a generator casing. Thus, the concentric electrodes are not effective because the space is usually less than one inch. Also, should the center core electrode in U.S. Pat. No. 3,420,301 be reduced in diameter and the gap slightly increased there would still not be sufficient spacing. Further, if the center core electrode diameter were greatly reduced the electrode would not be able to withstand the current necessary to work with electrodes to produce adequate GPM's.